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🏗 Interview Prep

System Design

Scaling, caching, databases, queues and the classic "design X" questions, each with a diagram you can step through.

📘 Learn it from scratch

Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.

Scaling from 1 to 1 Million UsersCaching Strategies & Building an LRU CacheLoad BalancersDatabases at Scale: Replication & ShardingQueues & Background JobsAcing System Design Interviews (+ Rate Limiter)

100 questions, most asked first

Ranked by how often each question comes up in real interviews. #1 is the most common.

Any difficulty Easy Medium Hard

All patterns Design interview Scaling basics Caching Load balancing Databases at scale Consistent hashing CAP & consistency Queues & async Rate limiting CDNs & storage Real-time Reliability

#5Scaling the databaseDatabases at scaleHardFree #6Consistent hashingConsistent hashingHardFree Unlock 46 more System Design questions · all 1,200 questions for $39/year (about 11¢ a day)See full access #11Design a chat app (like WhatsApp)Real-timeHard🔒#12Design a news feed (like Twitter or Instagram)Design interviewHard🔒#14Design search autocomplete (backend)Design interviewHard🔒#15Design a web crawlerDesign interviewHard🔒#16Design a distributed cache (like Redis Cluster)CachingHard🔒#17Design a photo-sharing app (like Instagram)Design interviewHard🔒#18Design a video platform (like YouTube)CDNs & storageHard🔒#19Design a ride-sharing app (like Uber)Real-timeHard🔒#20Design a ticket booking system (like Ticketmaster)CAP & consistencyHard🔒#22Design a distributed key-value storeCAP & consistencyHard🔒#23Design a payment systemDesign interviewHard🔒#25Design file sync (like Google Drive or Dropbox)CDNs & storageHard🔒#26Design a metrics and alerting systemReliabilityHard🔒#28Design an online code judge (like LeetCode)Queues & asyncHard🔒#36Distributed transactions and the saga patternQueues & asyncHard🔒#38Sharding strategiesDatabases at scaleHard🔒#39Bloom filtersCachingHard🔒#40Leader election and consensus (Raft)CAP & consistencyHard🔒#44Going multi-regionCAP & consistencyHard🔒#45Backpressure and load sheddingReliabilityHard🔒#46Scaling WebSockets to millions of connectionsReal-timeHard🔒#47The transactional outbox patternQueues & asyncHard🔒#48CQRS and event sourcingDatabases at scaleHard🔒#49Hot keys and the thundering herdCachingHard🔒#51Design a collaborative editor (like Google Docs)Real-timeHard🔒#53Design a distributed job scheduler (cron at scale)Queues & asyncHard🔒#55Design an ad-click counter at massive scaleQueues & asyncHard🔒#56Design an e-commerce cart and checkoutCAP & consistencyHard🔒#57Design live comments for a stream (like Twitch chat)Real-timeHard🔒#58Design a recommendation systemDesign interviewHard🔒#65Strong, eventual and read-your-writes consistencyCAP & consistencyHard🔒#66B-tree vs LSM-tree storage enginesDatabases at scaleHard🔒#67At-most-once, at-least-once, exactly-onceQueues & asyncHard🔒#72Design price alerts (stocks or flights)Queues & asyncHard🔒#73Design an email service (like Gmail)Databases at scaleHard🔒#75Design a distributed message queue (like Kafka)Queues & asyncHard🔒#78Design video calling (like Zoom)Real-timeHard🔒#79Design maps and turn-by-turn routing (like Google Maps)Design interviewHard🔒#84Distributed locksCAP & consistencyHard🔒#85Time, clocks and ordering eventsCAP & consistencyHard🔒#87Heartbeats, failure detection and gossipReliabilityHard🔒#88Cache invalidation strategiesCachingHard🔒#91Design trending topics (top-K heavy hitters)Queues & asyncHard🔒#92How does object storage (like S3) work?CDNs & storageHard🔒#95Design a banking ledgerCAP & consistencyHard🔒#96Design a food delivery appReal-timeHard🔒